1. Field of the Invention
This invention relates to an electronic musical instrument capable of performing portamento.
2. Description of the Prior Art
Perfect portamento for electronic musical instruments is generally considered a function which continuously changes the tone pitch of a musical tone to be generated from the tone pitch specified by a previously depressed key to the tone pitch specified by the presently depressed key. For example, such perfect portamento is shown on the line A of FIG. 2.
In order to perform portamento in prior art electronic musical instruments, in addition to a keyboard, a portamento bar, for example, has been used. So as to perform the portamento, a player slides his finger on the portamento bar and, before the tone pitch of the musical tone generated by the portamento bar reaches a final tone pitch, switches his finger from the portamento bar to a key of the keyboard corresponding to the final tone pitch. Thereby, the player tries to perform the perfect portamento.
However, since it is necessary to play so that the tone pitches of generated musical tones are smoothly changed in the time it takes to shift from the portamento bar to the keyboard, the execution of this kind of playing is very difficult.
Furthermore, in the case of performing portamento only by a keyboard without the portamento bar, at least two different keys need to be depressed before the portamento is performed. That is, since the initial and final tone pitches must be determined, the problem is that the portamento starts only after the second key depression has almost been finished as shown on the line B of FIG. 2. Since the portamento in which the tone pitch continuously changes starts after the tone pitches of the previously depressed key and the presently depressed key (2nd key operation) are determined, a delay occurs between the second key depression and the actual sound generation corresponding to it, resulting in unnatural playing.